1. Field of the Invention
The present invention relates to a lighting apparatus capable of changing its light emission direction, and more specifically, a lighting apparatus, such as a reading light, attached to, for example, a seat in transportation means, such as railroad wagons, airplanes and ships.
2. Description of the Related Art
As a lighting apparatus of this type, a down light is known in which, for example, a light fitting of a substantially spherical shape is rotatably held by a substantially cylindrical light main body, thereby enabling the direction of light emission to be changed (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2005-149790). When assembling the down light, the light fitting is mounted on the edge of a circular opening that is formed in the light main body by narrowing the inner periphery of the body, and then a plate spring is attached to the light fitting from behind to press it against the edge of the opening.
With this structure, the light fitting is held stationary by the frictional force exerted between the edge of the circular opening of the light main body and the spherical outer surface of the light fitting, and that of the back surface of the light fitting and the plate spring. Further, when an external force is applied to the light fitting to change its orientation, the outer surface of the light fitting is slid along the edge of the circular opening, with the result that the orientation of the light fitting is changed. By virtue of this structure, the emission direction of an LED contained in the light fitting can be changed.
In this type of lighting apparatus, the outer surface of the light fitting is slid along the edge of the circular opening of the light main body when the orientation of the light fitting is changed. However, the above-mentioned publication has no description concerning problems that may occur after such sliding is again and again repeated during long-term use.
Further, the publication describes that the light main body having the circular opening is a resin molded product or an aluminum die-cast product, but does not describe the material of each component of the light fitting. Namely, it is unclear what types of materials are used for the sliding portions of the light main body and light fitting.
If the sliding portions of the light main body and light fitting are both metal members, the following problem will be raised. In general, to smooth the sliding, the outer surface of the light fitting is coated with another metal. However, the metal coating is gradually worn away while the orientation of the light fitting is repeatedly changed. When abrasion of the coated layer has advanced, the metal ground layers of the two components are exposed and brought into direct contact with each other. At this time, galling of the ground layers occurs to degrade the sliding performance, with the result that it becomes difficult to smoothly change the orientation of the light fitting.
In contrast, if the sliding portions of the light main body and the light fitting are both resin members, the coefficient of dynamic friction therebetween is relatively low, and hence the light fitting can slide relatively smoothly during its rotation. However, in this case, the coefficient of static friction is relatively high. Therefore, when the light fitting is in a static condition, it is hard to smoothly start the rotation of the same without harsh frictional noise. Further, it is known that the degree of friction between resin members changes in accordance with the ambient temperature, and that the higher the temperature, the greater the coefficient of static friction.
Moreover, when the light main body and the light fitting are both resin members, the heat dissipation performance is degraded. Namely, since resins have much lower heat conductivity than metals, if the light fitting is formed of a resin, the heat produced by the LED of the fitting cannot be efficiently dissipated. This being so, to obtain heat dissipation performance sufficient to maintain the emission efficiency of the LED, it is necessary to make the light fitting large. This is another problem.